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Re: Some concern about the journal support

From: Bean
Subject: Re: Some concern about the journal support
Date: Sun, 15 Jun 2008 00:17:57 +0800

On Sat, Jun 14, 2008 at 7:43 PM, Robert Millan <address@hidden> wrote:
> On Fri, Jun 13, 2008 at 04:14:17PM -0400, Pavel Roskin wrote:
>> Your patch should fix the issue with hardcoding block locations, if I
>> understand correctly.
> Notice that hardcoding block locations only happens when core.img doesn't
> fit in the post-mbr area.
> Which is a situation we should try to avoid by making core.img small, which
> means a smaller ext2.mod also helps ;-)
>> I was asking where journal support would be beneficial in userspace at
>> all.  And it has to be asked if journal support is useful at the boot
>> time.
>> We have some code that is hard to get right and hard to test.  Yet it
>> will be run every time an unclean ext3 filesystem is found at the boot
>> time.  What are we gaining?  What is the situation where using the
>> journal is beneficial?  How likely is it to happen?  Is it possible that
>> we may be better off not using the journal?  How likely is that?
>> The standard use of the journal is to make the filesystem consistent
>> after an unclean shutdown without having to run a time-consuming fsck.
>> Since grub is not writing anything to the disk, consistency is not
>> really important.  What's important got grub is reliability and ability
>> to access all files on the filesystem.
>> > btw, the reiserfs driver is a little strange, it don't follow the
>> > normal path of grub_fshelp_read_file, perhaps we just disable the
>> > journal at the moment.
>> My impression is that we need to make journal support experimental and
>> disabled by default for both ext3 and reiserfs.  It should only be
>> enabled by default if there are a good arguments why it's useful and a
>> testsuite to prove that it's reliable.
> How about a separate module?


It's a good idea, perhaps I can add a journal layer on top of disk to
do the mapping transparently.


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